1. Field of the Invention
The present invention relates to a thin film magnetic head constructed by laminating component parts such as a magnetic core, a coil and the like on a substrate using a thin film forming process, and a magnetic tape drive including this thin film magnetic head as a recording/reproducing head for recording/reproducing signals on and from a recording tape.
2. Description of Related Art
Conventionally, as a recording head for recording signals on a magnetic recording medium, a so-called bulk type magnetic head has been employed, which forms a magnetic circuit therein by disposing a pair of magnetic cores made of a magnetic material opposite to each other to form a small magnetic gap therebetween, and by winding coils around the pair of the magnetic cores for generating a magnetic field passing therethrough.
Further, along with the recent advancement in the high density recording, a so-called metal-in-gap (MIG) type magnetic head has been used in practice, in which a metal magnetic thin film with a high saturation magnetic flux density is deposited on opposed surfaces of a pair of magnetic cores made of ferrite or the like, which are, then, disposed adjacent to each other via a nonmagnetic film to provide a magnetic gap therebetween.
Generally, the recording head supplies a current in response to a recording signal to its coil, then a magnetic field generated from the coil allows its magnetic flux to pass through the pair of magnetic cores, thereby producing a recording magnetic field across the magnetic gap so that by applying this recording magnetic field to the magnetic recording medium, the signal is recorded thereon.
By the way, in this type of the recording head, in order to meet with a demand for a higher density recording capability, it has become increasingly important to have a narrower track width and improve accuracy of processing of this track width. However, as there is a limit in the manufacture of the aforementioned magnetic head using a micro fabrication technique, it has become increasingly difficult further to a narrower the track width corresponding to the demand for the higher density recording capability.
Therefore, a so-called thin film magnetic head has been proposed as a recording head capable of meeting with the demand for the higher density recording capability, which can be constructed by laminating various component parts on a substrate using a thin film process. This type of the thin film magnetic head has such advantages that, as their constituting elements such as a magnetic core, a coil and the like can be formed by a thin film forming method such as plating, sputtering, ion milling or the like, advantageous micro fabrication of narrower tracks, a narrower gap or the like becomes easier, thereby enabling to reduce the size of the device and improve the recording density in the magnetic recording medium.
An exemplary construction of the thin film magnetic head will be described with reference to FIGS. 19, 20 and 21.
This thin film magnetic head 100 is fabricated by laminating a lower magnetic core layer 102 and an upper magnetic core layer 103 on a substrate 101, which form a magnetic circuit. Each of the lower magnetic core layer 101 and the upper magnetic core layer 103 has a protrusion 102a and a protrusion 103a, respectively, formed at its end on the side of a medium facing surface 100a opposing a magnetic recording medium, protruding with each predetermined track widths Tw1′ and Tw2′, wherein by positioning the protrusions 102a and 103a via a nonmagnetic layer 104 oppositely and adjacent to each other in the direction of lamination, a magnetic gap G′ is formed. Further, at its other end remote from the medium facing surface 100a in a depth direction therefrom, the lower magnetic core layer 102 and the upper magnetic core layer 103 are connected to form a back gap. Then, a thin film coil 105 is formed between the lower magnetic core layer 102 and the upper magnetic core layer 103 in a state being wound around this back gap and embedded in the nonmagnetic layer 104. An end of the thin film coil 105 at an inner periphery of the coil and the other end thereof at an outer periphery of the coil are extended externally in an opposite direction from the medium facing surface 100a to external connection terminals 105a and 105b for connection with an external circuit. Further, as an uppermost layer of the substrate 101, a protection layer 106 is provided to cover the whole surface area excepting a portion where the external connection terminals 105a and 105b of the thin film coil 105 are exposed.
Further, among this type of thin film magnetic head 100, in order to meet with a demand for a still more improved high density recording capability, there is such one as shown in FIG. 22, in which, in addition to its narrowed track width, its lower magnetic core layer 102 has a protrusion 102b protruding therefrom adjacent and corresponding to a protrusion 103a of a upper magnetic core layer 103. In this thin film magnetic head 100, by counter-positioning the protrusion 102b on the lower magnetic core layer 102 corresponding to the protrusion 103a on the upper magnetic core layer 103 adjacent to each other in the direction of lamination via a nonmagnetic layer 104, a magnetic gap G′ is formed therebetween, and also their widths are formed corresponding to track widths Tw1′ and Tw2′. As described above, according to the thin film magnetic head 100 shown in FIG. 22, in which the protrusion 102b is formed on the lower magnetic core layer 102, to have a width corresponding to a width of the protrusion 103a on the upper magnetic core layer 103, a leakage magnetic flux from a side surface in the direction of the track width, i.e., a side fringing can be reduced. By suppressing an adverse effect of this side fringing, a stabilized effective track width can be obtained.
According to the above thin film magnetic head 100, as each component element thereof is formed on the substrate by means of the thin film process, it has become possible to obtain a narrower width track and respond to the demand for a still further improved high density recording on the magnetic recording medium. Accordingly, this thin film magnetic head 100 which has been initially used as a recording/reproducing head for a high density magnetic recording/reproducing apparatus in a magnetic disk drive including a hard disk drive (HDD) is now being used for a magnetic tape drive such as a video tape recorder (VTR) and the like as well.
By the way, in the above magnetic tape drive represented by the VTR or the like, it is common to use a helical scan system. In the magnetic drive using the helical scan system, a magnetic tape runs in a state being helically wound in a predetermined range of angles around an outer periphery of a rotary drum. Further, a pair of recording heads is mounted on this rotary drum with its magnetic gap exposed to outside from the outer periphery thereof. Therefore, in this helical scan system, when the rotary drum is driven to rotate while the magnetic tape runs helically relative to the rotary drum, the pair of recording heads mounted on the rotary drum are enabled to scan helically or obliquely the magnetic tape.
Further, in this magnetic tape drive, whereas one of the pair of the recording heads mounted on the rotary drum applies a magnetic field in response to a recording signal on the magnetic tape so as to form a recording track thereon with a predetermined track width, the other one of the pair of the recording heads applies a magnetic field in response to a recording signal on the magnetic tape so as to form another recording track with a predetermined track width at a position adjacent to the previous recording track formed thereon as described above. Then, by operating the pair of the recording heads to form recording tracks on the magnetic tape in repetition, recording tracks written by the one of the pair of the recording heads and other recording tracks written by the other one of the pair of the recording heads are formed alternately on the magnetic tape.
Further, in this magnetic tape drive, by writing a following recording track to slightly overlap a previously written recording track, a non-recorded region between adjacent recording tracks, i.e., a so-called guard band is eliminated so as to improve the recording density in the magnetic tape.
In addition, in this magnetic tape drive, as the pair of the recording heads are disposed in such a manner that each magnetic gap is slanted relative to a direction orthogonal to a scanning direction of the recording head corresponding to an azimuth angle, and that each azimuth angle is set an opposite phase to each other, an interference between adjacent recording tracks, i.e., a cross talk is suppressed to minimum. This kind of recording method described above is generally referred to as the azimuth recording.
[Patent Document 1]
Japanese Patent Application Publication Laid Open No. 2001-236605 (page 4, FIG. 3) is referred to in the description of the present invention.
By the way, in the magnetic tape drive performing the above-mentioned azimuth recording, when the thin film magnetic head 100 described above is used as its recording head, there is likely to arise a problem of a so-called side erase in which a part of an adjacent recording track is erased.
The side erase is caused mainly by a leakage magnetic flux from a side surface in a direction of the track width described above, i.e., a side fringing, in a non-azimuth recording with no azimuth angle, and if such a side erase occurs in a recording track, there arises a problem that an S/N ratio drops because its reproducing head cannot read out signals sufficiently from the recording track. Further, in a case of the azimuth recording, as the thin film magnetic head 100 which is the pair of the recording head is disposed obliquely corresponding to the azimuth angle, its leakage magnetic flux generated from the side surface in the direction of the track width will have substantially a greater degree of influence as the side fringing in comparison with that in a case of the non-azimuth recording.
Further, in a case of the thin film magnetic head 100 as shown in FIG. 22, even if its side fringing is reduced so that the influence thereof the side fringing becomes negligible, a side erasing may take place owing to the azimuth recording.
More specifically, according to this thin film recording head 100, it is normally arranged such that a recording bit once recorded by a recording magnetic field generated at the protrusion 102b on the side of the lower magnetic core layer 102 which is positioned on a so-called leading side in a scanning direction of the head is re-recorded by a recording magnetic field generated at the protrusion 103a on the side of the upper magnetic core layer 103 which is positioned, opposite the leading side, on a so-called trailing side. Then, in the case of the azimuth recording, as the thin film magnetic head 100 is disposed obliquely corresponding to the azimuth angle as shown in FIG. 23, there occurs a deviation in a direction orthogonal to the scanning direction of the head, namely, in the direction of a track width, between the protrusion 102b on the side of the lower magnetic core layer 102 which is positioned on the leading side and the protrusion 103a on the side of the upper magnetic core layer 103 which is positioned on the trailing side.
In this case, in a recording track formed on the magnetic tape by the thin film magnetic head 100, there arises such a problem that, because of a deviation in the direction of the track width between a recording magnetic field generated by the protrusion 102b on the side of the lower magnetic core layer 102 which is positioned on the leading side and a recording magnetic field generated by the protrusion 103a on the side of the upper magnetic core layer 103 which is positioned on the trailing side, a recording bit is recorded which inevitably includes a phase difference between a track width Tw1′ of a recording bit recorded by the recording magnetic field generated at the protrusion 102b on the side of the lower magnetic core layer 102 and a track width Tw2′ of a recording bit recorded by the recording magnetic field generated at the protrusion 103b on the side of the upper magnetic core layer 103, thereby reducing an effective track width of this recording bit.
Further, there occurs another problem in this thin film magnetic head 100 that along with the narrowing of the track, its side erase region increases gradually relative to a track pitch, thereby deteriorating its S/N ratio further.